Retarded person on the internet who spams you with the entire alphabet, either correct or not, ending it with Z.
It can also refer to people who mis-spell almost every word or every other word and add or replace a letter with Z for no apparent reason. Most of these people can be found on common sites like Myspace, Gaiaonline, Youtube, or any other large site that can show local text by the public.
Most are doing it just to annoy you.
Others are just that stupid.

Today, I was going on Myspace to check my messages when I found the most ridiculous Z-tard that I almost commited genocide.

Any software programmer who works for Zynga, which produces the worst software on Earth, and also the management at Zynga, that either tolerates incompetence or requires it.

Zynga has the same promotions every week, and you would think they could copy and paste, but Nooooo, the Z-Tards always have new bugs. Any software coded by a Z-Tard has more bugs than the Brazilion rain forest.